ML20126E858
| ML20126E858 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 07/23/1974 |
| From: | JERSEY CENTRAL POWER & LIGHT CO. |
| To: | |
| References | |
| AO-50-219-74-38, NUDOCS 8103040459 | |
| Download: ML20126E858 (2) | |
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.ersey Central Povyer & Lig t Comoany MADISON AVENUE AT PUNCH BOVA. ROAD e MORRISTOWN, N.J. 07960
- 201-533 6111
...a, a un General hjj((, Public Utitilies Corpotalson
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0YSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 Abnormal Occurrence Report No. 50-219/74/38 Report Date July 23, 1974 1
Occurrence Date July 14, 1974 Identification of Occurrence _
i' Violation of the Technical Specifications, paragraph 4.5.I.2, failure of the main steam isolation valve NSO4B Jo close in less than 10 seconds. This event l
is considered to be an abnormal occurrence as defined in the Technical Specifi-cations, paragraphs 1.15D and E.
Conditions Prior to Occurrence The reactor was shut down and reactor coolant temperature was approximately 160*F.
I Description of Occurrence During the routinc full closure surveillance test of the main steam isolation l
valves, performed as part of the prercquisites to a plant startup, it was observed that main steam isolation valve NSO4B closed in 13.0 seconds.
Two subsequent trials resulted in times of 8.0 and 8.5 seconds.
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Apparent Cause of Occurrence As a result of installation of the new pilot control system for the main stean isolation valves' air operators, throttling of the hydraulic speed control valves to some degree greater than with the former system appears to be necessary to j
control the closing speed for the valves. The increased throttling appears to j
have decreased somewhat the sensitivity of the hydraulic valves themselves.
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, Consequently, repeatability of the closing speeds is not as firm as it has been j
in the past.
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s Abnormal Occurrence No. 50-219/74/38 Page 2
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Analysis of Occurrence
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The 10 second maximum time for full closure of the main steam isolation valves is to provido a safety margin in the event of a main steam line break.
Closure of these valves minimizes the radioactive dose to the environs and provides for maintaining a coolant icvel above the fuel assemblies in the reactor without consideration of coolant makeup. systems.
The failure of one main steam isolation valve to close in the required time removed the system redundancy.
If a steam line break had occurred, NS03B would have isolated the system in the required time.
i Corrective Action In order to climinate any question as to the operability of the new main steam isolation valve pilot modifications, the four-way valve in the pilot valve assembly was inspected, cicaned and relubricated.
Following reinstallation, the valve was retested but still did not close within the required time.
The hydraulic needle valves were then adjusted to give the required closing speed. Action had previously been initiated to purchase more sensitive hydraulic valve stems to permit better throttling characteristics.
However, the valve stems purchased were not sized properly for the actual hydraulic valves installed.
Since installation of the modified pilot assemblies, new hydraulic valves have been ordered.
Current plans are to install these units during the first shutdown (where drywell entry is allowed) following receipt of the new valves.
Failure Data Not applicable, r
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